1. Field of the Invention
The present invention relates to a backlight apparatus used in a Liquid Crystal Display (LCD), more particularly, which has upper and lower reflective plates installed under upper and lower transparent plates, respectively, in such a fashion that the lower transparent plates and the lower reflective plates introduce light generated by lower light sources in upward directions and the upper transparent plate and the upper reflective plates introduce light generated by an upper light source into those areas, which are not lighted by the lower light sources, in order to prevent the formation of dark areas above the lower light sources as a problem of a conventional large-sized backlight apparatus, thereby enhancing the overall uniformity of light. In this way, the backlight apparatus of the invention can be designed thin even when applied to a large-sized LCD.
2. Description of the Related Art
LCD backlight apparatuses using Light Emitting Diodes (LEDs) illuminate an LCD panel via direct illumination or side-emitting illumination. In the side-emitting illumination, light from a light source is emitted in lateral directions and then re-directed upward via a reflective plate or a scattering pattern to illuminate the LCD panel. On the contrary, in the direct illumination, light sources are installed under the LCD panel so that light emitted laterally from the light sources are projected upward onto the LCD panel.
FIG. 1 is a schematic cross-sectional view of a conventional side-emitting backlight apparatus. As shown in FIG. 1, the side-emitting backlight apparatus includes a sheet-shaped reflective plate 12 having a scattering pattern 14 formed thereon, a light guide plate 16 placed on the reflective plate 12 and bar type LED light sources 18 and 20 placed at both sides of the light guide plate 16.
The LED light sources 18 and 20 emit light L laterally into the light guide plate 16. Then, light L propagates through the light guide plate 16, and when colliding against the scattering pattern 14, is scattered upward thereby backlighting an LCD panel 22 above the light guide plate 16.
The side-emitting backlight apparatus 10 as above advantageously has a thin and simple structure. Another advantage of this backlight apparatus is that the intensity of light directed upward can be uniformly adjusted through the design of the scattering pattern 14 formed in the top face of the reflective plate 12 or the underside of the light guide plate 16. However, this structure is not applicable to a large-sized LCD since light from the LED light sources 18 and 20 can be sent to a limited distance only.
FIG. 2 is a schematic cross-sectional view of a conventional direct-illumination backlight apparatus. The direct-illumination backlight apparatus 30 includes a sheet-shaped reflective plate 32, a plurality of bar-shaped LED light sources 34 placed on the reflective plate 32, flat light shades 36 placed on the LED light sources 34, respectively, a transparent plate 38 placed above the light shades 36 at a predetermined gap G1 and a diffuser plate 40 placed above the transparent plate 38 at a predetermined gap G2.
The LED light sources 34 emit light L substantially in horizontal directions, and emitted light L is reflected from the reflective plate 32 and passes through the transparent plate 38. Then, light L is diffused by the diffuser plate 40 to a desired uniformity to backlight an LCD panel 44 placed above the diffuser plate 40. The backlight apparatus 30 of this structure has an advantage in that it can effectively backlight a large-sized LCD since the plurality of bar-shaped LED light sources 34 are placed under the LCD panel 42.
However, the backlight apparatus 30 of this structure disadvantageously increases thickness since the gap G1 is required between the LED light sources 34 and the transparent plate 38 and the gap G2 is also required between the transparent plate 38 and the diffuser plate 40.
Describing it in more detail, when generated from the LED light sources 34, light L is reflected upward through first areas A1 and A2 between the light shades 36, such that second areas B1, B2 and B3 screened by the light shades 36 form dark areas and resultant bright lines. In order to remove the dark areas and the bright lines, the gap G2 is required to have at least a predetermined dimension to ensure a sufficient distance between the transparent plate 38 and the diffuser plate 40 so that light beams emitted upward through the first areas A1 and A2 from the transparent plate 38 can mix together before entering the diffuser plate 40.
As described above, since the gaps G1 and G2 are necessarily maintained at predetermined dimensions or more in order to impart uniformity to light directed from the reflective plate 32 toward the LCD panel 42, the direct-illumination backlight apparatus 30 essentially suffers from increase in thickness.